A muxponder (from “multiplexing transponder”) is a device that maps a plurality of low data rate input optical signals into a single higher data rate optical signal. The modulation format and line code can, generally but not necessarily, be different for the input and output signals. Although the concept is simple, the implementation of a muxponder can be very complicated. Before multiplexing the tributary signals in the time domain to form an output data frame at higher speed, they must first be converted from the optical to the electrical domain, and then they need to be synchronized and resampled. Overhead bits needed for error correction and maintenance functionalities must also be added. In order to improve link distance or spectral efficiency, conversion to multi-level modulation formats may be required. At ultra high speed data rates (400 Gbit/s and 1 Terabit/s) the implementation of all these functionalities is very challenging, due to the bandwidth limitations introduced by the opto-electronic devices used when converting the signals between the optical and electrical domains.